The modern backhoe, sometimes called a "pull shovel", is of a design which results from combining the most desirable features taken from the prior art steam shovel and drag line.
The prior art steam shovel bucket is rigidly affixed to a movable boom and is arranged to cut or excavate while going upwardly and away from the machine. This arrangement causes the bucket to work at a mechanical disadvantage and the weight of the machine must therefore be greater than the resulting forces encountered while making the cut. Moreover, the machine must be positioned in its own excavation so that it works at the bottom of the cut.
The drag line, on the other hand, digs in opposition to the shovel, with its bucket suspended from a boom by a series of cables so that the bucket is swung away and pulled towards the machine. The drag line works above its cut thereby enabling it to excavate a relatively narrow trench of varying depth as well as enabling it to work in water or mud. The drag line provides the mechanical advantage of working below and pulling the bucket toward the machine. The operation is not directly dependent upon the weight of the machine in order to effect the pull of the cut. The major disadvantage found in the drag line is the inability to precisely position and control the bucket because of its cable suspension arrangement. Furthermore, the downward digging force applied to the bucket is dependent upon the weight thereof as well as the skill of the operator.
The modern backhoe is a combination of recent advances in hydraulics along with the most desirable features found in the steam shovel and the drag line. The backhoe bucket is affixed to a movable boom and is turned in a direction to make the cut towards the backhoe machine. The bucket boom is arranged to enable the machine to be positioned on top of the cut, thereby providing the mechanical advantage of disposing the bucket so that it cuts from below and towards the machine.
Before the advent of modern hydraulics, the backhoe depended upon weight and brute force for proper performance of its digging function. Modern hydraulic systems have substantially reduced the weight of the machine, thereby eliminating the need for a heavy bucket and boom. Modern hydraulics also enables the bucket to be movably affixed to the boom, thereby enabling the cutting edge of the bucket to be continually adjusted for optimum alignment regardless of the position of the boom.
With the exception of being made lighter, backhoe buckets have remained essentially unchanged from the original design created from the combination of features taken from the steam shovel and the drag line bucket. In order for the backhoe bucket to penetrate the material to be excavated, it is essential that the digging teeth thereof be placed in aligned relationship on the lower flat surface of the leading edge of the bucket. The magnitude of force required to effect penetration of the bucket into the earth is related to the number and location of teeth. The fewer the teeth, the more difficult is the pulling of the bucket. Therefore, a compromise has heretofore been necessary in selecting the number of teeth to be employed on the prior art bucket.
The area of the bucket lip which is not covered by excavating teeth must be forced into the ground with a tearing effect. This represents a tremendous expenditure of power. Formations such as soapstone, will not easily tear or shatter as it is penetrated by the teeth, but instead, the individual teeth form a series of spaced grooves. As the lip of the bucket contacts the ridges between the spaced grooves, the digging can no longer proceed. The tremendous forces required by the tearing effect therefore limits the amount of work a specific backhoe can achieve.
Conventional backhoe buckets are tapered with the bucket being wider at the leading edge as compared to the trailing edge thereof. The teeth usually are arranged to simultaneously cut on the same plane; and accordingly, when the bucket encounters damp or muddy conditions, a substantially solid cube of material is torn loose and forced back into the tapered bucket. Hence, this design is satisfactory for excavating dry material, but is undesirable for digging into wet material because the cube of removed material is tightly packed within the tapered interior of the bucket. Hence, movement of the bucket into the uncurled configuration fails to empty the bucket because the excavated material sticks to the sidewalls thereof and refuses to be discharged therefrom.
Digging in wet or plastic-like material represents one of the major problems associated with the backhoe. Digging in hard formations, such as the above example of soapstone, presents a similar problem to the backhoe. It would therefore be desirable to have made available a backhoe bucket of a design which represents a definite step forward in overcoming the above-recited problems. The solution to this problem is the subject of the present invention.